The present invention relates to an exposure apparatus, and more particularly to an exposure apparatus that exposes an object, such as a single crystal substrate and a glass plate for a liquid crystal display (“LCD”). The present invention is suitable, for example, for an exposure apparatus that uses extreme ultraviolet (“EUV”) light for an exposure light source.
Conventionally, during manufacturing, photolithography technology, a reduction projection exposure apparatus using a projection optical system to project a circuit pattern formed on a reticle (mask) onto a wafer, etc., has been employed for transferring the circuit pattern of fine semiconductor devices such as semiconductor memory and logic circuit.
The minimum critical dimension transferred by the projection exposure apparatus or resolution is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the better the resolution. Thus, along with recent demands for finer semiconductor devices, shorter ultraviolet light wavelengths have been proposed—from an ultra-high pressure mercury lamp (I-line with a wavelength of approximately 365 nm) to KrF excimer laser (with a wavelength of approximately 248 nm) and ArF excimer laser (with a wavelength of approximately 193 nm).
However, lithography using ultraviolet light has limitations when it comes to satisfying the rapidly promoted fine processing of a semiconductor device. Therefore, a reduction projection optical system using extreme ultraviolet (“EUV”) light with a wavelength of 10 to 15 nm shorter than that of the ultraviolet (referred to as an “EUV exposure apparatus” hereinafter) has been developed to efficiently transfer very fine circuit patterns of 100 nm or less.
Since materials greatly absorb the light of a wave range of the EUV light, a refractive optical system (that utilizes lenses or refractions of light) for use with visual light and UV light is not viable because of the low transmittance of the EUV light to an optical element, such as a lens. Therefore, a catoptric optical system is used which utilizes reflections of light. A reticle also uses a reflection reticle that uses an absorber on a mirror to form a pattern to be transferred.
The EUV light is strongly absorbed by a gas. For instance, when the EUV light propagates a space filled with an air of 10 Pa by 1 m, the EUV light of about 50% is absorbed. It is necessary to maintain the space to which the EUV light propagates to a pressure of at least 10−1 Pa or less, desirably 10−3 Pa or less, to evade the absorption of the EUV light by the gas.
Moreover, carbon compounds found in air, such as hydrocarbons, remains in a space that an optical member (for example, a mirror and reticle) irradiating the EUV light is arranged, the carbon gradually adheres to the surface of the optical member. As a result, reflectivity decreases because the carbon absorbs the EUV light. It is necessary to maintain the space where the optical member irradiating the EUV light is arranged to a pressure of at least 10−4 Pa or less, desirably 10−6 Pa or less, to prevent the carbon adhering to the surface of the optical member.
An exposure apparatus that considers these things is proposed in Japanese Laid-Open Patent Application No. 07-263322 and Japanese translation of PCT international application No. 2002-529927.
However, the exposure apparatus repeats an operation that carrying the wafer coated with a resist from the outside into the exposure apparatus, then transfers the circuit pattern of the reticle onto the wafer, and carrying out of the exposure apparatus. A wafer stage has a transport mechanism composed of a movement mechanism for a scanning exposure and carrying mechanism that carries the wafer. Therefore, as for the wafer stage, creating a high vacuum is extremely difficult because of the surface area increases and out gas generated from these parts.
Moreover, the resist spread on the wafer is an carbon compound which has been heated before the exposure. Then, when the wafer is carried in the vacuum, the carbon compound that is the resolved material, etc. that compose the resist evaporate, and it diffuses in the apparatus maintained to the vacuum. The wafer is carried from an atmosphere to the inside of the exposure apparatus, so according to carrying the wafer, losing an atmospheric constituent, which includes moisture that adheres to the wafer, in a short time is difficult. The atmospheric constituent desorbs gradually in the vacuum. It is very difficult to maintain the inside of the exposure apparatus to the high vacuum because of the out gas from the wafer and resist.
The vacuum can be improved with a mass vacuum pump etc., but it is necessary to prevent the carbon compound and the moisture to diffuse in the exposure apparatus, especially in the space that the mirror and the reticle are arranged.